Temperature-dependent Photoluminescence Studies Research Articles

Distinct Valley Polarization in Vertical Heterobilayers: Difference between Edge- and Center-Nucleated WS2/MoS2.

Structural imperfections can cause both beneficial and detrimental consequences on the excitonic characteristics of transition metal dichalcogenides (TMDs). Regarding valley selection, structural defects typically promote valley depolarization in monolayer TMDs, but defect healing via an additional growth process can restore valley polarization in vertical heterobilayers (VHs). In this study, we analyzed the valley polarization of center-nucleated and edge-nucleated VHs (WS2/MoS2) grown using a controlled growth process and discovered that defect-related photoluminescence (PL) is strongly suppressed in the center-nucleated VHs due to defect healing. Additionally, we demonstrated that the valley polarization of lower-lying intralayer excitons is more sensitive to the defect density of the sample than to higher-lying intralayer excitons. Despite defect healing in the center-nucleated VHs, the temperature-dependent PL study indicated that valley depolarization of the lower-lying intralayer excitons becomes significant below 100 K because of stronger hybridization of defect states. Also, we conducted a comprehensive study on the excitation intensity dependence to investigate the electron-doping-induced Auger recombination mechanism, which also contributes to valley depolarization of intralayer excitons via regeneration of intervalley trions. Our findings provide valuable insight into the development of VH-based valleytronic devices.

Robust luminescent material with superior color purity: Sm3+ ion-doped CaAl4O7 phosphor synthesized in a cost-effective approach for solid-state lighting applications

This work reports the synthesis of Sm3+ ion doped calcium dialuminate phosphor by microwave-assisted combustion synthesis technique. Phase purity and the crystal structure of the phosphors were affirmed by PXRD analysis and was found to have monoclinic structure. SEM study was performed to analyze the surface morphology. FTIR study clarifies the existence of functional groups. The optical bandgap of 4.43 eV was determined for CaAl4O7:Sm3+ (x = 0.03) sample. The emission spectra of the sample recorded upon excitation at 403 nm suggest orange color emission around 601 nm pertaining to the transition 4G5/2→6H7/2 of Sm3+ ions. The optimal dopant concentration was established at 3 mol%. CIE chromaticity coordinates of (x = 0.6029, y = 0.3964) were established for the optimized sample. Correlated color temperature of 1620 K demonstrates the emission of light in warmer region. The superior color purity of 99.21 % and color rendering index of 77 for the optimized phosphor material was manifested. The photoluminescence (PL) decay time (for Sm3+ concentration = 0.03 mol) was found to be 0.73 ms. Thermal stability of the sample was investigated and the activation energy was determined to be 0.152 eV by temperature-dependent PL study. To explore the lighting ability of the phosphor, phosphor-in-glass (P-i-G) material was fabricated. CaAl4O7:Sm3+ (x = 0.03) based P-i-G material validates excellent luminous efficacy (360 lm/W) and luminous efficiency (52.70 %) which affirms its practical applications.

Tackling toxicity and stability using eco-friendly metal-halide ion substituted perovskite nanocrystals for advanced display color conversion

In recent years organic–inorganic hybrid halide perovskites nanocrystals have made a remarkable impact in display color converting layer application. However, lead toxicity and stability issues always pose arduous challenges. In this regard, the incorporation of a suitable metal ion to reduce toxicity and enhance stability is a widely tested method. In this study, we used a simple ligand-assisted reprecipitation (LARP) technique to simultaneously introduce metal ion and halide ion substitution by synthesizing MAPb1-xZnxBr3-2xCl2x nanocrystals (NCs). Being eco-friendly with a smaller ionic radius than lead ion, zinc metal ion was chosen as a substitute. With the variation of Zn2+ concentration, the highest quantum yield of 95 % was recorded with an emission width of 21 nm. Temperature-dependent photoluminescence (PL) studies revealed the higher optical phonon-exciton interaction after Zn2+ incorporation leading to radiative transition in NCs. Variation of PL peak energy with temperature revealed the reduced thermal chromaticity of Zn2+ incorporated NCs making them suitable for display application. Further, these NCs maintained a stable cubic structure and luminescence up to 150 °C, indicating higher thermal stability. The MAPb0.9Zn0.1Br2.8Cl0.2 (x = 0.1 or 10 mol%) NCs embedded in PMMA (poly (methyl methacrylate) polymer matrix coated LED emits narrow width, green light with color coordinate (0.15, 0.79), which is closer to green coordinate (0.17, 0.79) in Rec.2020. This helps to reproduce close to 97 % color gamut of Rec.2020. This research paves the way for finding less toxic and stable green light-emitting materials instead of cadmium-based molecules.

Shedding Light on Host-to-Yb3+ Energy Transfer in Cs2AgBiBr6:Yb3+ (nano)crystals.

The optical properties of Cs2AgBiBr6 double perovskite nanocrystals have attracted considerable attention as lead-free alternatives to lead halide perovskites. A promising strategy to create additional flexibility in the emission color is doping lanthanide ions into Cs2AgBiBr6. Incorporating Yb3+ in the lattice has been shown to give rise to near-infrared (NIR) emission, but the energy transfer mechanism remained unclear. Here, we report on the luminescence and sensitization mechanism of Yb3+ in Cs2AgBiBr6 nano- and microcrystals. We observe that the incorporation of Yb3+ in the host lattice does not strongly affect the broadband red emission of the Cs2AgBiBr6 host but does give rise to an additional and characteristic ∼1000 nm NIR line emission from Yb3+. Temperature-dependent and time-resolved photoluminescence studies of undoped and Yb-doped Cs2AgBiBr6 reveal that the energy transfer does not take place through the red emissive state of the Cs2AgBiBr6 host. Instead, there is a competition between relaxation to the red-emitting state and trapping of the photoexcited charge carriers on Yb3+. Trapping on Yb3+ subsequently results in a charge transfer state that relaxes to the 2F5/2 excited state of Yb3+, followed by NIR narrow line f-f emission to the 2F7/2 ground state.

Colour-tunable features in thermally stable Tb3+/Eu3+ co-doped telluro tungstate glasses for photonic applications

The melt quenching procedure has been followed to synthesize transparent Tb3+ singly activated and Tb3+/Eu3+ co-activated TeO2–WO3–K2O–ZnO–Bi2O3 (TWKZBi) glasses. The structural characteristics of the prepared TWKZBi glass samples were examined through x-ray diffraction. The existence of functional units corresponding to the different vibrations has been examined via Raman spectroscopy. The photoluminescent characteristics and energy transfer (ET) analysis in the Tb3+/Eu3+ co-activated TWKZBi glasses were investigated in depth. Several emission peaks have been observed in Tb3+ doped TWKZBi glasses under n-UV and blue excitations and the maximum luminescent intensity has been detected for 2.0 mol% of Tb3+ doped TWKZBi glass sample. The emission spectra of co-doped Tb3+ and Eu3+ ions in the TWKZBi glasses have been studied, and the maximum ET efficiency is found to be 32.82% under n-UV excitation. The ET from sensitizer (Tb3+) to activator (Eu3+) ions happen through dipole–dipole interaction, as confirmed by Dexter’s and Reisfeld’s approximation. The colour-tunable emission in the prepared glass samples can be achieved via varying the content of activator ions. The decay profiles for the 5D4 level of Tb3+ ions diminish with varying the concentration of Eu3+ ions, confirming the ET from Tb3+ to Eu3+ ions. Furthermore, temperature-dependent photoluminescence studies show that the Tb3+/Eu3+ co-doped TWKZBi glasses have good thermal stability. All the aforementioned results reveal the suitability of the Tb3+/Eu3+ co-activated TWKZBi glass samples for photonic applications.

(Poster Award - 2nd Place) Layer-Number Engineered Momentum-Indirect Interlayer Excitons with Large Spectral Tunability

The diversity of two-dimensional (2D) materials provides van der Waals heterostructures with abundant degrees of freedom and makes the family a promising candidate to realize novel optoelectronic devices and an attractive platform for exploring physical phenomena. Interlayer excitons in type-II van der Waals heterostructures are equipped with an oriented permanent dipole moment and long lifetime and thus would allow promising applications in excitonic and optoelectronic devices. However, in the widely studied van der Waals heterostructures constructed by transition metal dichalcogenides, the formation of interlayer excitons is limited by the lattice mismatch, rotational and translational alignment between the constituent layers, increasing the complexity of the device fabrication. Here, I will report on the robust momentum-indirect interlayer exciton emission with widely tunable emission energy via layer engineering in transition metal dichalcogenide/2D perovskite heterostructures. The transition metal dichalcogenides with different thicknesses and 2D perovskites with different layer numbers of the inorganic octahedral slabs are stacked to form type-II van der Waals heterostructures without considering special orientation arrangement and momentum mismatch. The presence of interlayer excitons is supported by the excitation-power- and temperature-dependent photoluminescence studies, photoluminescence excitation spectroscopy, time-resolved photoluminescence decay studies and electric field-dependent photoluminescence studies. Taking advantage of the thickness- or layer-number-dependence of the electronic band structure of the constituent materials, the emission energy of the interlayer excitons in our heterostructures can be tuned from 1.3 eV to 1.6 eV, providing strong evidence for the applications of van der Waals interface engineering to broad-spectrum optoelectronics. In addition, the diffusion coefficient of interlayer excitons in our heterostructures can be estimated to be ~10 cm2 s−1, which is at least one order of magnitude larger than that in the van der Waals heterostructures with Moiré superlattice, suggesting a non-localized nature that would be beneficial to the excitonic devices. Our study would offer new insights into the nature of interlayer excitons and provoke further research into their dynamics.

Exploring the potential of Sm3+-doped Sr2B2O5 phosphors for bridging the amber gap in w-LED application

A series of orange-red emitting Sr2(1-x)B2O5:2xSm3+(x = 0.5–3.0 mol%) phosphors have been synthesized via the self-propagating low-cost solution combustion method. The purpose of this study is to address the amber gap in light-emitting diodes (LEDs). X-ray diffraction technique was employed for structural analysis, which reveals the creation of a purely monoclinic phase having space group P21/a. The optical characteristics of synthesized Sr2B2O5:Sm3+ phosphor were investigated via Photoluminescence (PL) and UV–Vis spectroscopy. The findings of the PL studies indicate that the phosphors doped with Sm3+ ions exhibit distinct emission peaks at 565 nm, 604 nm, 649 nm, and 712 nm when excited by a wavelength of 404 nm. These peaks are ascribed to electronic transitions from 4G5/2 to 6HJ (J = 5/2, 7/2, 9/2, 11/2) energy levels. The temperature-dependent PL studies suggest that the synthesized phosphors display a remarkable thermal stability of 96.1 % and 90 % at 150 ℃ and 200 ℃, respectively. The Diffused Reflectance Spectrum was utilized to estimate the optical band gap energy. The CIE coordinates (0.6, 0.39) for the phosphors were found to be in the orange-red region exhibiting a towering color purity of 98.6 %. The aforementioned findings demonstrate the prepared phosphors will be an auspicious candidate for amber LEDs for automotive illumination.

Size- and temperature-dependent optical, and electron field emission characteristics on SnO2 nanocrystals

Size-dependent SnO2 nanocrystals (NCs)) were synthesized using a co-precipitation technique. The particle size was varied by annealing the as-prepared SnO2 NCs with the estimated size of 2.3 nm at different temperatures. The particle size obtained was 4.7, 9.0, 15.4, 19.6, and 48.0 nm at annealing temperatures of 400, 600, 800, 1000, and 1200 °C, respectively. The XRD data revealed the tetragonal rutile structured for all SnO2 NCs. The temperature-dependent photoluminescence (PL) studies showed that the sub-bridging oxygen vacancy contributed dominantly compared to the in-plane and bridging oxygen vacancies at 5K. The function of nanocrystals’ size on field emission properties is also reported. The current density was high (1.9 μA/cm2) with modest the turn-on field (8.4 V/μm) for as-prepared SnO2 QDs with the lowest size (2.3 nm) compared to the high temperature annealed SnO2 nanocrystals.

Tailoring Carbon Tails of Ligands on Au52(SR)32 Nanoclusters Enhances the Near-Infrared Photoluminescence Quantum Yield from 3.8 to 18.3.

One of the important factors that determine the photoluminescence (PL) properties of gold nanoclusters pertain to the surface. In this study, four Au52(SR)32 nanoclusters that feature a series of aromatic thiolate ligands (-SR) with different bulkiness at the para-position are synthesized and investigated. The near-infrared (NIR) photoluminescence (peaks at 900-940 nm) quantum yield (QY) is largely enhanced with a decrease in the ligand's para-bulkiness. Specifically, the Au52(SR)32 capped with the least bulky p-methylbenzenethiolate (p-MBT) exhibits the highest PLQY (18.3% at room temperature in non-degassed dichloromethane), while Au52 with the bulkiest tert-butylbenzenethiolate (TBBT) only gives 3.8%. The large enhancement of QY with fewer methyl groups on the ligands implies a nonradiative decay via the multiphonon process mediated by C-H bonds. Furthermore, single-crystal X-ray diffraction (SCXRD) comparison of Au52(p-MBT)32 and Au52(TBBT)32 reveals that fewer methyl groups at the para-position lead to a stronger interligand π···π stacking on the Au52 core, thus restricting ligand vibrations and rotations. The emission nature is identified to be phosphorescence and thermally activated delayed fluorescence (TADF) based on the PL lifetime, 3O2 quenching, and temperature-dependent PL and absorption studies. The 1O2 generation efficiencies for the four Au52(SR)32 NCs follow the same trend as the observed PL performance. Overall, the highly NIR-luminescent Au52(p-MBT)32 nanocluster and the revealed mechanisms are expected to find future applications.

Tb3+/Mn4+ co-doped SrLaMgNbO6 green/red dual-emitting phosphors for optical thermometry

Remote and noncontact surface temperature measurements are frequently required yet challenging to execute. One the most promising options consists in using rare earth or transition metal doped materials as optical (luminescence) temperature sensors. In this paper, a series of novel Tb3+/Mn4+ co-doped SrLaMgNbO6 (SLMN) phosphors have been synthesized and thoroughly investigated for their structural, luminescence spectroscopic and decay kinetics properties as well as for temperature sensing performance. X-ray powder diffraction (XRD) analysis has shown that the prepared sample presents a double perovskite structure. Upon the UV excitation, emission spectra of SLMN:Tb3+, Mn4+ exhibit green and red emission bands for Tb3+ and Mn4+ dopants, respectively. Temperature-dependent photoluminescence (TD-PL) studies revealed sever thermal quenching of Mn4+ emission while that of Tb3+ was moderate providing well pronounced difference in fluorescence intensity ratios (FIR) of the ions. The maximum relative sensitivity (Sr) was found to be 3.27% K−1 and 1.92% K−1 for Mn4+ and Tb3+, respectively. This implies that SLMN: Tb3+, Mn4+ phosphor is a viable candidate material for a dual-mode optical temperature detection.

Luminescence properties of Tb3+/Eu3+ ions activated LiLaSiO4 phosphors for solid-state lighting and flexible display applications

The synthesis and luminescence properties of Tb3+ and Eu3+ single- and co-doped LiLaSiO4 (LLSO) phosphors with energy transfer mechanisms were reported. The rare-earth ions doped LLSO phosphors were synthesized via a solid-state reaction method and their physical characterizations such as phase purity, surface morphology, and elemental analysis were investigated systematically. For the Tb3+ and Eu3+ single- and co-doped LLSO phosphors, their photoluminescence (PL) properties were studied in detail. The LLSO:Tb3+ and LLSO:Eu3+ single-doped phosphors showed superior red and green emissions due to 5D4→7F5 and 5D0→7F2 in the optimized characteristic electronic transitions under ultraviolet (UV) irradiation, respectively. The luminescence performances for both the LLSO:Tb3+ and LLSO:Eu3+ phosphors were optimized at 0.125 mol of doping ion concentration. Under UV excitation, by adjusting the Eu3+ ion concentration in LLSO:0.125Tb3+/Eu3+ phosphors, the tunable emissions from green to red via yellow-orange were obtained. Thus, the tunable emission spectra and luminescence decay lifetimes with increasing the doping content of acceptor ions (Eu3+) confirmed an efficient energy transfer from Tb3+ to Eu3+ ions in the co-doped samples. The critical distance between Tb3+ and Eu3+ was determined to be 13.26 Å and the energy transfer mechanism from Tb3+ to Eu3+ ions was demonstrated to be a dipole-dipole mechanism interaction. In addition, the temperature-dependent PL study was carried out for the LLSO:0.125Tb3+/0.025Eu3+ co-doped phosphor sample and it showed better thermal stability against the temperature quenching. The Tb3+ and Eu3+ single- and co-doped LLSO/polydimethylsiloxane (PDMS) flexible composite films were fabricated by mixing the phosphor powders and PDMS solution. Benefiting from the effective protection of the PDMS matrix, the luminescence stability of the composite films was greatly enhanced. Based on the excellent properties of the synthesized phosphors, Tb3+ and Eu3+ single-doped and Tb3+/Eu3+ co-doped LLSO phosphors could serve as a single-phase multicolor-emitting phosphor under UV excitations.

Binding of CsPbBr3 Nanocrystals to MOF-5 for the Detection of Cadmium Ions in Aqueous Media

CsPbBr3 perovskite nanocrystals (CNCs) have emerged as promising candidates for optoelectronics, although instability issues have retarded their progress toward commercialization. As a solution to this core issue, herein CNCs are bound to the metal–organic framework MOF-5 to form a stable composite MOF:CNC for sensing applications in aqueous media. The electrostatic interaction of Pb2+ and Br– ions of CNCs with the terephthalate and Zn2+ ions of MOF-5 do not disturb the structural integrity of the MOFs and the photoluminescence (PL) properties of the CNCs but renders more stability to both the MOFs and CNCs in a water medium. As a proof-of-concept experiment, this water-resistant MOF:CNC probe was successfully validated for the detection of Cd2+ in a water medium. The mechanism of fluorescence enhancement during the sensing of Cd2+ is elucidated using X-ray photoelectron spectroscopy, temperature-dependent, and time-resolved PL studies. The high stability and photoefficiency exhibited by this MOF:CNC composite proves that it is a viable system for applications in aqueous media.

Luminescence properties and energy transfer studies in thermally stable Bi2O3: Sm3+, Eu3+ phosphor

The advent of innovative rare-earth based metal oxide phosphors has prompted increasing interest in the search for highly efficient red emitting phosphors for various optoelectronic devices, lighting and display applications and motivated the research community to develop some promising, state-of-the-art, and potential red phosphors to meet the necessary requirements. In this study, a series of Sm3+ (1–7 mol%) doped, Sm3+ (5%) doped and Eu3+ (2–5 mol%) co-doped Bi2O3 red phosphors were synthesized by a facile urea assisted auto-combustion process. The X-ray diffraction (XRD) analysis of the phosphors ascertains the tetragonal crystal structure without any trace of impurity. The UV-Vis-NIR absorption study of the phosphors was carried out in 200–1000 nm range and the estimated optical band gap of the phosphors was lying in the range of 2.778–2.831 eV. The photoluminescence (PL) emission studies were performed at an excitation wavelength of 481 nm in the 550–720 nm range. The effective energy transfer mechanism from Sm3+ to Eu3+ in the Bi2O3 phosphor has been ascribed to the dipole-dipole (d-d) interaction. The energy transfer process was further validated by PL decay time measurements. The CIE color coordinates were obtained using PL emission data. The CIE chromaticity diagram ascertains that the emission color of Bi2O3: Sm3+ phosphors were tuned from reddish-orange to the red region by varying the concentration of Eu3+ ions. The temperature dependent PL study of the phosphors was taken out in the range of 293–453 K and was found thermally stable at elevated temperatures.

Thermally stable Sm3+ -doped alkali zinc alumino borosilicate (AZABS) glass for warm white light generation and w-LED applications.

Samarium ion (Sm3+ )-doped alkali zinc alumino borosilicate (AZABS) glass was synthesized via quick melt quench technique. Various spectroscopic studies like optical absorption, photoluminescence (PL) emission, PL excitation, temperature-dependent PL and PL decay kinetics were performed on the as prepared glass system. Under 402 nm excitation, three sharp bands at wavelengths 563, 599 and 645 nm corresponding to transitions 4 G5/2 → 6 H5/2 , 6 H7/2 and 6 H9/2 , respectively, can be seen in the PL emission spectra. The 0.25 mol% Sm3+ glass has the highest intensity for these emissions. The lanthanide interaction in the glass matrix is dipole-dipole in nature as was proven from Dexter's analysis. The direct bandgap of 0.25 mol% Sm3+ -doped AZABS glass was calculated to be 2.88 eV. The lifetimes of the as prepared glass range from 1.93 ms for the lowest concentration of Sm3+ to 0.75 ms for the highest. From temperature dependent PL studies, the activation energy for 0.25 mol% Sm3+ -doped AZABS glass was found to be 0.19 eV which shows high thermal stability of this glass. We propose to utilize these Sm3+ -doped AZABS glasses for white-light emitting diodes (w-LEDs) and solid-state lighting (SSL) applications.

Charge Carrier Recombination Dynamics in MAPb(BrxCl1-x)3 Single Crystals.

Understanding carrier recombination processes in MAPb(BrxCl1-x)3 crystals is essential for their photoelectrical applications. In this work, carrier recombination dynamics in MAPb(BrxCl1-x)3 single crystals were studied by steady-state photoluminescence (PL), time-resolved photoluminescence (TRPL), and time-resolved microwave photoconductivity (TRMC). By comparing TRPL and TRMC, we find TRPL of MAPb(BrxCl1-x)3 (x < 0.98) single crystals is dominated by a hole trapping process while the long-lived component of TRMC is dominated by an electron trapping process. We also find both electron and hole trapping rates of MAPb(BrxCl1-x)3 (x < 0.98) crystals decrease with an increase in Br content. A temperature-dependent PL study shows there are shallow trap states besides the deep level trap states in the MAPb(Br0.82Cl0.18)3 crystal. The activation energy for holes in shallow trap states detrapped into the valence band is ∼0.1 eV, while the activation energy for free holes to be trapped into deep trap states is ∼0.4 eV. This work provides insight into carrier recombination processes in MAPb(BrxCl1-x)3 single crystals.

Multicolor tunable bright photoluminescence in Ca2+/Mg2+ modified Eu3+ doped ZnGa2O4 phosphors under UV excitation for solid state lighting applications.

The Eu3+ doped and Mg2+/Ca2+ co-doped ZnGa2O4 phosphor samples were synthesized by solid-state reaction method and their structural and optical properties studied. The phase, crystallinity and particles size of the phosphor samples were studied by XRD and SEM measurements. EDS analyses were used to identify the elements present in the phosphor materials. The vibrational groups present in the phosphor samples were examined by Fourier transform infrared (FTIR) measurements. Pure ZnGa2O4 emits intense blue light under 260 nm excitation. However, Eu3+ doped and Mg2+/Ca2+ co-doped ZnGa2O4 phosphor samples exhibit intense red emission under 393 nm excitation. A bluish white color is observed in these samples under 290 nm excitation. The maximum PL emission intensity is found at 0.1 mol% Eu3+ doping concentration. For higher concentrations, concentration quenching was observed due to dipole-dipole interaction. The emission intensity is enhanced upto 1.20 and 2.91 times on co-doping of Mg2+ and Ca2+via induced crystal field due to charge imbalance. The emission intensity of the phosphor is found to enhance further on annealing the samples at 873 K. Under various excitation wavelengths, color tunability was seen from blue to bluish-white to red regions. The lifetime of the 5D0 level of the Eu3+ ion improves via doping of Mg2+/Ca2+ ions and it increases appreciably on annealing. The temperature dependent photoluminescence study (TDPL) reveals a thermal quenching behavior of the sample with thermal stability ∼65% and activation energy ∼0.223 eV in the Eu3+/Ca2+ co-doped ZnGa2O4 phosphor sample.

Thermally stable red luminescence from Eu3+ -activated telluro zinc phosphate glass under near-ultraviolet light excitation for photonic applications.

Telluro zinc phosphate (TZP) glasses doped with different concentrations of Eu3+ ions were prepared and their physical, structural, and luminescence properties were studied in detail to reveal the utility of the as-prepared glass for white light-emitting diode (w-LED) applications. The broad hump in the diffraction pattern specified the amorphous behaviour of the TZP glass. The various vibrational shoulder linkages were characterized using the Fourier transform infrared (FT-IR) spectroscopy. The optical absorption spectrum was measured in the ultraviolet (UV)-visible (Vis) light region for the Eu3+ -doped TZP (TZPE) glass and the optical band gap was found to be 3.12 eV. Eu3+ -doped TZP glasses showed several emission peaks in the visible region including an intense red emission peak due to the 5 D0 →7 F2 transition under an excitation wavelength of λex = 393 nm, which was matched with the emitting wavelength of the near-UV LED chip. Commission Internationale de I'Eclairage (CIE)chromaticity coordinates were situated in the red region and nearly matched with the coordinates of the commercial red phosphor (Y2 O3 S:Eu3+ ). The decay profile of the TZPE50 glass exhibited a single exponential fit with a decay time ( of 1.76 ms. Temperature-dependent photoluminescence (TDPL) studies demonstratethat the as-prepared glass consist of excellent thermal stability. The detailed analysis and results confirmed that the red-emitting TZPE glasses were potential candidates for white-LED and other photonic applications.

Observation of strong electron-phonon interaction in polymeric diluted organic semiconductor

Incorporating organic semiconductors in insulating polymer films, creating the so‐called diluted organic semiconductors, has been successfully used in different optoelectronic devices, including organic light-emitting diodes. However, the fundamental understanding of their excited state dynamics and spin physics remains elusive. Here, we present the temperature-dependent photoluminescence (PL) and transient absorption study of a model fluorescent organic dilute semiconductor where organic fluorophore pyrene is incorporated in the insulating Poly-methyl methacrylate (PMMA) polymeric backbone as pendant unit (py-PMMA). We observe that by lowering the temperature from 300 K to 140 K, the monomer fluorescence emission from py-PMMA gets blue-shifted, and their intensity enhances, which is attributed to less charge carrier scattering lattice sites at low temperature. Interestingly, we observe additional higher energy peaks at 368 nm (∼3.36 eV) below 70 K in fluorescence emission, explained by the exciton-phonon coupling. The exciton-phonon interaction constant (γph) is determined as 168 µeV/K, higher than other reported systems. The transient absorption measurement reveals the hot band relaxation (τ1 = 1.9 ps) and exciton- acoustic phonon interaction (τ2 = 27.2 ps) dominating in the excited state. Our study establishes that the electron–phonon interaction can play significant role in determining the optoelectronic properties of the fluorescent dilute organic semiconductor.

Spectroscopic characterizations of Dy3+ ions doped phosphate glasses for epoxy-free white LED applications

The present work illustrates a detailed spectroscopic analysis carried out on dysprosium ions doped Zinc Alumino Sodium Phosphate (ZnAlNaP) glasses with chemical composition of (10-x)ZnO–20Al2O3–10Na2O–60P2O5-xDy2O3 (x = 0.1–2.0 mol%). The XRD spectra verified for an un-doped and Dy3+ ions doped ZnAlNaP glasses demonstrate an enormous hump confirming its amorphous behavior. The FT-IR and Raman spectrum recorded for an un-doped ZnAlNaP and ZnAlNaPDy1.0 glass elucidates various functional groups and vibrational modes involved, respectively. The DSC & TGA studies conducted on an un-doped ZnAlNaP glass revealed its thermal stability and overall weight loss. The absorption spectra were used to calculate the optical bandgap for the as-synthesized glasses and were found to be in the range of 2.9 eV–4.7 eV. Photoluminescence (PL) excitation, emission and decay spectral analysis were done to investigate the suitability of the as-synthesized glasses for epoxy-free solid-state lighting (SSL) devices. The PL emission recorded under 350 nm excitation show two significant bands in blue and yellow regions. Temperature-dependent PL studies conducted on ZnAlNaPDy1.0 glass revealed activation energy of 0.212 eV with a 25.6% loss in PL intensity. The CIE color chromaticity coordinates and correlated color temperature (CCT) were calculated from the PL spectral characteristics. All the spectroscopic investigations conducted on the as-synthesized ZnAlNaPDy glasses finally reveal their superior nature for fabricating epoxy-free white-light emitting diodes (w-LEDs).

Structural and optical properties of cubic GaN on U-grooved Si (100)

Cubic GaN epitaxy on large-area U-grooved silicon (100) dies is demonstrated by metalorganic chemical vapor deposition, and its structural and optical properties are reported. Scanning electron, atomic force, and transmission electron microscopy studies reveal that cubic GaN shows no discernible threading dislocations and a low stacking fault density of 3.27 ± 0.18 × 104 cm−1. Temperature-dependent photoluminescence studies reveal as-grown cubic GaN band edge emission internal quantum efficiency as 25.6% ± 0.9%. Selective etching of the low-temperature AlN buffer layer, SiO2 sidewalls, and hexagonal-phase GaN is demonstrated, which increases the cubic GaN band edge emission internal quantum efficiency to 31.6% ± 0.8%. This increase is attributed to the decrease in the radiative recombination lifetime via the removal of defective hexagonal-phase GaN. Overall, cubic GaN on U-grooved silicon with high structural and optical quality is reported, promising its suitability for next-generation devices.